L-161 IM Design Technologies - Gun Propellants
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The general characteristics and design constraints/considerations for Gun Delivery Systems are widely varied in some instances and yet common in many others. Although achievement of IM is a systems design issue, whilst the IM characteristics of a munition are determined by a wide range of factors, there are several aspects of gun charge components that are common to consider as related factors. These typically include the properties of the energetic compositions (particularly explosiveness, sensitivity and damage tolerance), the case (material, thickness and construction) and its degree of confinement, the initiation and safety train, the use of active and passive mitigation techniques and the packaging immediately adjacent to the munition.
A systems approach is needed to meet the requirements because different characteristics of the system and of the components are involved in meeting the criteria. Such an approach entails a coordinated program involving the development of less sensitive propellants and ignition charges together with cases, packaging and venting devices that mitigate the response to energetic stimuli. As the test series required by the IM standards is expensive to conduct on full scale components, and may give inconsistent results, improvements are needed in techniques to predict the response of the components in the delivery system, based on a good understanding of the material properties and component configurations.
Gun delivery systems appear to have a reasonably medium profile, in practice the development and manufacturing costs are a significant proportion of the overall munition costs. For instance, the cost of a propelling charge might be perhaps 30 – 60% of the shell it projects. Recently in some instances, this proportion is decreasing with the introduction to service of the new precision guided ammunition. Moreover, in considering the attention given in designing the munition or weapon, the efforts to provide full IM compliance may be only secondary or tertiary priority to the other competing performance aspects driving the design.
We review the IM state of the art of gun propellant charge systems for medium and large calibre indirect and direct fire gun systems. Some of the information presented here is discussed in further detail in the NIMIC report L-94 Edition 2 and in the MSIAC report L-135. It is recommended that the reader examine L-94 and L-135 in conjunction with this sub-chapter. Care should be taken in making use of this review to ensure that the solutions identified in it take into account the performance requirements and other constraints associated with the munition system of which the propelling charge is part.
The present document updates information given in the NIMIC report IM Design Technology (L-101) gun propulsion section. The main changes concern the list of IM technologies available and the shortfalls.